1. Field of the Art
The present invention relates to a spray tower or cooling, moistening and/or purifying a gas. More particularly, the present invention relates to a dry spray tower and method whereby water and/or an absorbing solution is sprayed by a spray nozzle attached in the vicinity of the top of the spray tower, thereby cooling and moistening a gas and/or removing a harmful component from the gas without producing waste water.
2. Prior Art
To cool and moisten a gas and/or remove a harmful component from the gas, a dry spray tower has heretofore been used. FIG. 5, for example, shows a typical conventional dry spray tower in which the gas 5a is introduced into the tower from the top 1 thereof through an expanded portion 2 and sprayed with water and/or an absorbing solution by a spray nozzle 4 attached in the vicinity of the top of the tower, and in which the sprayed water and/or absorbing solution is completely evaporated in the tower so that no waste water is produced. In such a spray tower, a swirling motion is often given to the gas when introduced into the tower.
The conventional technique suffers, however, from the problem that liquid droplets sprayed in the vicinity of the top of the spray tower collide with the inner wall of the tower and the liquid flows down as far as the bottom, resulting in waste water.
That is, in the conventional spray tower, as shown in FIG. 5, the flow velocity of gas is relatively fast in the central portion of the tower at a position immediately downstream from an expanded portion 2 through which the exhaust gas is introduced into the tower, whereas it is relatively slow in the peripheral portion of the tower. Therefore, at the downstream side of the expanded portion 2, the gas whirls up from the central portion toward the peripheral portion of the tower as shown by an arrow 5b. As a result, sprayed liquid droplets collide with the inner wall of the tower, giving rise to problems as described above. In particular, when the temperature of the exhaust gas, after the sprayed water and/or absorbing solution has evaporated, is lower than the dew point of the gas plus 50.degree. C., it is difficult for liquid droplets having collided with the inner wall to re-evaporate. Therefore, there is a very strong possibility that the liquid droplets colliding with the inner wall will flow down as far as the bottom to become waste water. Further, when the gas contains dust, the dust adheres to the inner wall wetted with the liquid droplets.
Further, in a case where a swirling motion is given to the gas when introduced into the spray tower, the centrifugal force induced by the swirl of the gas tends to encourage the collision of sprayed liquid droplets with the inner wall of the tower, which enhances the problem.
Therefore the object of the present invention is to solve the above-described problems of the conventional technique and to provide a spray tower and method for cooling, moistening and/or purifying a gas, wherein sprayed liquid droplets are prevented from colliding with the inner wall of the tower, thereby preventing generation of waste water and adhesion of dust to the inner wall of the tower.